1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device which is provided with a circuit including a semiconductor element such as a transistor. For example, the present invention relates to a power device which is mounted on a power supply circuit; a semiconductor integrated circuit including a memory, a thyristor, a converter, an image sensor, or the like; and an electronic device on which an electro-optical device typified by a liquid crystal display panel, a light-emitting display device including a light-emitting element, or the like is mounted as a component.
In this specification, a semiconductor device generally refers to a device which can function by utilizing semiconductor characteristics; an electro-optical device, a light-emitting display device, a semiconductor circuit, and an electronic device are all included in the category of the semiconductor device.
2. Description of the Related Art
Many transistors formed over a glass substrate or the like are manufactured using amorphous silicon, polycrystalline silicon, or the like, as typically seen in liquid crystal display devices. Although a transistor manufactured using amorphous silicon has low field-effect mobility, it can be formed over a larger glass substrate. On the other hand, although a transistor manufactured using polycrystalline silicon has high field-effect mobility, it cannot be formed over a larger glass substrate.
Other than the transistors manufactured using silicon, in recent years, a technique in which transistors are manufactured using an oxide semiconductor and applied to electronic devices or optical devices has attracted attention. For example, a technique in which a transistor is manufactured using zinc oxide or an In—Ga—Zn—O-based oxide as an oxide semiconductor and used for a switching element of a pixel of a display device or the like is disclosed in Patent Document 1 and Patent Document 2.